What to Plant in April – Northern Climate Edition

There’s something magical about April for us northern gardeners. The snow begins to retreat, revealing patches of soil that have been hidden for months. Tiny green shoots emerge from bulbs planted last fall, and suddenly, the gardening itch becomes impossible to ignore. But if you’ve gardened in a northern climate for any length of time, you know that April can be the cruelest month – teasing us with warm days only to plunge us back into freezing temperatures without warning.

This is the month where all our winter dreaming and planning finally meets soil, but in our shorter growing seasons, strategy isn’t just helpful – it’s essential. Those of us in northern climates don’t have the luxury of multiple growing seasons or forgiving winters. We need to make every week count.

The recommendations in this guide are specifically tailored for gardeners in zones with last frost dates in May (roughly USDA Hardiness Zones 2-5). If that’s you, April isn’t just another month in the garden calendar – it’s the critical launching pad for your entire growing season.

Understanding Frost Dates: The Northern Gardener’s North Star

Before we dive into what to plant, we need to talk about frost dates – the single most important piece of information for northern gardeners. Your last spring frost date and first fall frost date define your growing season, determining everything from when to start seeds to when to harvest.

What Exactly Is a Frost Date?

A frost date isn’t just a casual suggestion – it’s a statistical prediction based on historical temperature data. Specifically:

• Last spring frost date: The date after which there’s a 50% chance that temperatures won’t dip below 32°F (0°C) again until fall
• First fall frost date: The date when there’s a 50% chance that temperatures will drop to 32°F (0°C) or below

Notice the word “chance” in both definitions. This is crucial to understand – frost dates are probability statements, not guarantees. In northern climates especially, we need to work with these probabilities rather than against them.

Finding Your Specific Frost Dates

The USDA Hardiness Zone map provides a starting point:

• Zone 2: -50°F to -40°F (-45.6°C to -40°C) – Last frost typically late May to early June
• Zone 3: -40°F to -30°F (-40°C to -34.4°C) – Last frost typically mid-to-late May
• Zone 4: -30°F to -20°F (-34.4°C to -28.9°C) – Last frost typically early-to-mid May
• Zone 5: -20°F to -10°F (-28.9°C to -23.3°C) – Last frost typically late April to early May

But these are just general guidelines. For more precise information:

1. Check your local extension office website – These university-affiliated resources often provide county-specific frost date information based on decades of local data.
2. Use online frost date calculators – Tools like those offered by The Old Farmer’s Almanac or National Gardening Association can provide frost dates based on your zip code.
3. Ask your local nursery – This might be the most valuable resource of all! Local garden centers and nurseries have accumulated years of practical experience in your specific area. They can tell you not just the statistical frost dates but how reliable those dates have been in recent years. Many keep detailed records and can share insights about unusual patterns or recent shifts.
4. Connect with local gardening groups – Experienced gardeners in your community have invaluable knowledge about local conditions that no national database can match.

The Critical Importance of Microclimates

Here’s where gardening gets truly local – within any hardiness zone, and even within a single property, microclimates can create significant variations in frost risk. A microclimate is a small area where the climate differs from the surrounding area due to factors like:

• Elevation changes – Cold air flows downhill and settles in low spots, creating “frost pockets”
• Proximity to bodies of water – Lakes and rivers moderate temperature extremes
• Urban heat islands – Cities are often several degrees warmer than surrounding rural areas
• Building proximity – South-facing walls absorb heat during the day and release it at night
• Wind patterns – Areas sheltered from prevailing winds may be warmer
• Tree canopy – Mature trees can protect plants beneath them from light frosts

Your local nursery professionals can often help identify common microclimates in your region. They might tell you that gardens on the north side of your city typically see frost a week later than the official date, or that properties near the lake rarely get frost after mid-April despite what the charts say.

Understanding your property’s microclimates allows you to:

• Plant frost-sensitive crops in protected areas
• Utilize colder spots for crops that need chill hours
• Extend your growing season by weeks without additional protection

Cold-Hardy Veggies to Start or Direct Sow

With your frost dates firmly in mind, April offers northern gardeners plenty of planting opportunities. Once your soil temperature reaches about 40°F (4.5°C), these vegetables can either be started indoors or direct sown:

Brassicas: Broccoli, cabbage, cauliflower, and Brussels sprouts can all be started indoors now for transplanting later. These cool-season crops actually prefer the cooler temperatures of early spring and can tolerate light frosts once hardened off. For fall harvests of Brussels sprouts, April indoor starts are essential in northern zones to ensure enough growing time.

Leafy Greens: Spinach, kale, Swiss chard, and lettuce thrive in cool weather and can handle light frosts. Direct sow these once the ground can be worked, or start indoors for an earlier harvest. Consider succession planting lettuce every two weeks for continuous harvests before summer heat arrives.

Root Vegetables: Radishes, turnips, and kohlrabi can be direct sown as soon as soil can be worked. For carrots, beets, and parsnips, consider covering newly seeded areas with burlap or a light wood cover to maintain moisture during germination. Root vegetables generally dislike transplanting, so direct sowing is preferred when possible.

Potatoes: Whether in pots or ground, April is perfect for getting seed potatoes in the soil once it’s workable. In very cold areas, black plastic can help warm soil for earlier planting. Remember that potato foliage can be damaged by frost, so be prepared to cover young plants if late freezes threaten.

Peas: Direct sow toward the end of April when soil temperatures consistently reach 45°F (7°C). Peas are remarkably cold-tolerant and actually perform poorly in hot weather, making them perfect for northern spring gardens. Provide trellising at planting time to avoid disturbing roots later.

Onion Family: Onion sets, shallots, and leeks can all be planted in April. Onions are particularly sensitive to day length, so northern gardeners should select “long-day” varieties that form bulbs when daylight exceeds 14-16 hours.

Flowers to Start Indoors by Weeks Before Last Frost

Calculating backward from your last frost date allows for precise timing of flower seeds:

7 Weeks Before Last Frost:
Winged everlasting, asters (especially fall-blooming varieties), and delphiniums need this early start to establish strong root systems before transplanting. These early starts are crucial for northern gardeners who need flowers to reach maturity within our shorter growing seasons.

6 Weeks Before:
Nicotiana, Phacelia (Bee’s Friend), Nigella, candy tuft, and sweet alyssum. This is also the perfect time to start dahlias and cannas indoors or in cold frames. For dahlias especially, this indoor head start can mean the difference between August blooms and October blooms in zones 3-4.

5 Weeks Before:
Begin zinnias (some indoors, some outside if unusually warm), ornamental millet, Cleome (spider flower), and flowering kale. Early sunflowers can be started in a cold frame. Consider succession planting zinnias every 2-3 weeks through June for continuous blooms until frost.

4 Weeks Before:
Direct sow gladiolus (yes, even in cold soil—it works surprisingly well in northern gardens!). Start your second round of zinnias and cosmos, and either start indoors or direct sow marigolds, amaranth, penny black, and Rudbeckia. For northern gardeners, these timing windows are critical – start too late, and plants may not reach maturity before fall frosts arrive.

Use a Cold Frame for a Head Start

A simple cold frame can be your secret weapon for northern gardening success! This unheated structure with a transparent lid creates a microclimate that can be 5-10 degrees warmer than outside temperatures, effectively moving your garden one hardiness zone south. Use it for:

• Hardening off indoor seedlings gradually before transplanting
• Getting early growth on sunflowers and other heat-loving annuals
• Starting summer bulbs like Acidanthera and crocosmia weeks before outdoor planting
• Giving long-season crops like pumpkins, gourds, and melons the extra weeks they need to mature in our shorter growing season

Cold frames work by trapping solar heat and protecting plants from wind, creating a perfect transition space between indoor growing and the open garden. For northern gardeners, this intermediate step can extend the growing season by 4-6 weeks on both ends.

Real Talk on Weather & Flexibility

April in northern climates can swing wildly between spring-like days and sudden snow. I’ve seen 70°F (21°C) days followed by 6 inches of snow within the same week! This volatility means northern gardeners need both patience and flexibility.

Don’t put all your gardening eggs in one basket! The most successful northern gardeners use a mix of approaches:

• Start some plants indoors under lights
• Use cold frames and row covers for transition periods
• Direct sow when conditions allow
• Always keep some backup seedlings in case of late freezes

This multi-pronged approach provides insurance against unpredictable weather and extends your growing season significantly. Remember that in northern gardening, resilience matters as much as timing.

Common Mistakes to Avoid

Starting everything indoors: You’ll quickly run out of space and light. Be selective about what truly needs that head start, focusing on crops with long maturation periods or those that transplant easily.

Ignoring soil temperatures: Seeds have minimum germination temperatures. Cold, wet soil leads to rotting, not growing. Invest in a soil thermometer (they’re inexpensive) and follow temperature guidelines for each crop.

Planting in flooded or frozen ground: Working wet soil damages its structure for the entire season. Wait until a handful of soil crumbles when squeezed rather than forming a mud ball.

Skipping hardening off: Those tender seedlings need gradual introduction to outdoor conditions. Rush this process and you’ll lose plants to sunscald or cold shock. Plan for 7-10 days of progressive outdoor exposure.

Ignoring frost warnings: Even after your average last frost date, keep watching the forecast. Have row covers, cloches, or even old bed sheets ready to protect tender plants if late freezes threaten.

Keep a Planting Calendar

The single best tool for northern gardening success is a personalized planting calendar based on your specific frost dates, not generic months. This calendar should include:

• Your average last and first frost dates
• Dates to start seeds indoors (calculated backward from last frost)
• Safe transplanting windows for different crops
• Succession planting schedules
• Fall crop planting dates (calculated backward from first fall frost)

Track what works and what doesn’t each year, noting which varieties performed well in your specific conditions. Over time, you’ll develop a custom guide that’s worth its weight in garden gold.

Remember to consult with your local nursery professionals regularly. Their knowledge of regional conditions, successful varieties, and emerging weather patterns can help you refine your calendar year after year.

Happy planting, northern gardeners! Our shorter seasons may present challenges, but they also make each harvest all the more precious. With careful planning around frost dates and a good understanding of your local microclimates, your April plantings will set the stage for a bountiful growing season ahead.